The Solar Impulse (Si2) aircraft took off for a Round-The-World Flight fueled only by sunlight absorbed by the solar panels arrayed on its horizontal surfaces and carrying no backup fuel supply or alternative means of propulsion. Pilots André Borschberg and Bertrand Piccard began the first leg of the journey on the morning of March 9 from Abu Dhabi, UAE, headed for Muscat, Oman before crossing the Arabian Sea to Ahmedabad, India.

The Si2 aircraft is a single-seater made of carbon fiber. The solar-powered plane has 17,248 solar cells that supply the plane with renewable energy. The cells recharge four lithium polymer batteries totaling 633 kilograms (1,395 pounds) each. The plane has a 72-meter (236-foot) wingspan, larger than that of the Boeing 747, but weighs just 2,300 kilograms (5,070 pounds), about as much as a car. The Si2 is the largest aircraft ever built with such a low weight.

The event is 12 years in the making for Piccard, the development program’s initiator and chairman, and Borschberg, the founder and CEO. Capable of flying over oceans for several days and nights in a row, the Si2 is scheduled to travel 35,000 km (21748 miles) in 25 days over the course of roughly five months. The Si2 will pass over the Arabian Sea, India, Myanmar, China and the Pacific Ocean. After crossing the Atlantic Ocean, the final legs include a stop-over in Southern Europe or North Africa before completing the Round-the-World Flight at its final destination in Abu Dhabi. During the 12 scheduled stops, the Solar Impulse team and its partners will organize public events for governments, schools and universities.

Solar Impulse is an ambitious scientific project, say trip organizers, but the visionary journey is also a strong message for clean technologies. “We are very ambitious in our goal, but modest, given the magnitude of the challenge,” says Piccard and Borschberg. “This is an attempt, and only time will tell if we can overcome the numerous weather, technical, human and administrative issues.”